Page 1 of 2 12 LastLast
Results 1 to 13 of 22
  1. #1
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212

    Fusible link on a gas furnace?

    Rather than put a fuse on this furnace, an old Day & Night,
    the manufacturer stuck a small fusible link in the wire
    just before the heat exhanger limit switch. I amp'ed the
    line while the furnace was operating with the main
    gas valve open, burners burning, and it was less than
    1 amp. My first inclination is to put a 3 amp blade fuse
    inline rather than order the fusible link.

    Does doing so sound good or bad? The board has no
    other fuse for control voltage. I jumped it out
    with a 5 amp fuse and the furnace worked for three
    heat cycle attempts with the above amperage.
    Based on the above, I am inclined to believe the
    fusible link failed rather than really prevent a
    real high current hazard.

    The furnace is old, rusty, and could otherwise use
    replacement, but that isn't my decision.

    Thank you.
    =======

  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    it's called a fusible link for a reason


    clue: it's not amperage
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3
    Join Date
    Feb 2005
    Location
    GEORGIA
    Posts
    1,532
    I never ever, ever, modify a safety on a gas furnace........

    Many manufactures use a fuse link......

    I would take a long look at the heat exchanger......

    "Value our Differences"

  4. #4
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Quote Originally Posted by dandyme View Post
    it's called a fusible link for a reason


    clue: it's not amperage
    There are mechanical (heat sensitive) fusible links and
    there are electrical fusible links. It is my belief, since this
    is mounted about two inches from the surface of the
    heat exchanger, that it is an electrical fusible link, hence
    my reference to amperage. Thank you.

  5. #5
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,849
    that fusible link is not a fuse! it is a safety for the heating cycle. figure out why it did its job. if you remove the link you are liable for the death that may occur

  6. #6
    Join Date
    Feb 2004
    Posts
    2,458
    Quote Originally Posted by georgelass View Post
    Rather than put a fuse on this furnace, an old Day & Night,
    the manufacturer stuck a small fusible link in the wire
    just before the heat exhanger limit switch. I amp'ed the
    line while the furnace was operating with the main
    gas valve open, burners burning, and it was less than
    1 amp. My first inclination is to put a 3 amp blade fuse
    inline rather than order the fusible link.

    Does doing so sound good or bad? The board has no
    other fuse for control voltage. I jumped it out
    with a 5 amp fuse and the furnace worked for three
    heat cycle attempts with the above amperage.

    Based on the above, I am inclined to believe the
    fusible link failed rather than really prevent a
    real high current hazard.

    The furnace is old, rusty, and could otherwise use
    replacement, but that isn't my decision.

    Thank you.
    =======
    I believe you are confused about the function of a fusible link. They are designed to open on heat from a roll-out condition not high amperage. If you recall some of the older DNP products had 3 fuse links positioned on each side and above the heat exchanger opening. Probably not a bad idea to add a fuse to protect the system, now you must decide where is the best protection.
    When the fusible link on DNP products opens it brings the blower on.
    The reasons for continuous blower and no heat
    1. open rollout or limit
    2. bad transformer
    3. fuse link
    4. bad board

    The reason the furnace came on after install fuse, you closed the circuit, but left out the safety device.

  7. #7
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Quote Originally Posted by mike3 View Post
    I believe you are confused about the function of a fusible link. They are designed to open on heat from a roll-out condition not high amperage. If you recall some of the older DNP products had 3 fuse links positioned on each side and above the heat exchanger opening. Probably not a bad idea to add a fuse to protect the system, now you must decide where is the best protection.
    When the fusible link on DNP products opens it brings the blower on.
    The reasons for continuous blower and no heat
    1. open rollout or limit
    2. bad transformer
    3. fuse link
    4. bad board

    The reason the furnace came on after install fuse, you closed the circuit, but left out the safety device.
    There are not three of these strategically located. This single one is merely
    inline with the wire to the limit switch. This particular one looks
    most like a ceramic fusible link--actually, it looks like a resistor but
    I don't have my notebook with me to look it up anywhere--and
    all of the little ceramic fusible links I see online are rated by amperage,
    not temperature. I'm open-minded to this, but the evidence seems
    to point towards electrical protection, not temperature protection.

    Thank you. I do appreciate your efforts. You are absolutely right--I
    am confused, but I'm simply not yet convinced that it is about the
    electrical versus temperature function of fusible links. I know there
    are both kinds. I simply think this one is electrical.

  8. #8
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,849
    something like this that hooks to the main hi limit right?

    Name:  fuselink.JPG
Views: 1476
Size:  31.4 KB

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,736
    it is thermal protection.

    carefully inspect HX and flue.

  10. #10
    Join Date
    Feb 2005
    Location
    GEORGIA
    Posts
    1,532
    I believe, Trane uses a fuse link like Bro. George is talking about.....wish I had picture capabilities, I ordered three from Trane and got three boxes of 5......tried to send some back, but, they said it would be a hassele....lol...

    They are the same size as a traditional limit or fan switch but have a one time fuse in them.....
    Your furnace has issues.....
    "Value our Differences"

  11. #11
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Yes, that is roughly the same except it looks a lot newer and
    more modern.

    I swear i did a forum search on fusible link before posting this
    question but got nothing. But trying a google search, I found
    this one post:

    http://hvac-talk.com/vbb/showpost.ph...7&postcount=13

    It certainly seems strange that it would be so far from the burners!
    I've seen flames blow out enthusiastically from burners before and
    they did not roll up the face of the heat exchanger. I suppose having
    the doors off the unit changes the flames. That would make sense.

    Thanks again to all who tried to help me see this, even those who
    did not give much background! Sorry, but I'm from the Show-Me
    state so I like some convincing.

  12. #12
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,849
    i dont have pictures but, i got a service call about 3-4 years ago on a boiler. i turned the stat on. walked down to the basement turned the boiler switch on and watched it fireup and had all flames rolling out the heat exchanger and up the front of it. it melted the spark ignition box and wires but still fired up. it had no safeties. if there were a fuse link it would have shutdown the boiler

  13. #13
    Join Date
    Dec 2007
    Posts
    4,696
    it is NOT electrical, but heat activated.

    as has been stated, if it is bad, look for a flame issue!!!!!!!

    Google search, http://www.google.com/search?q=day+a...ient=firefox-a, came up with this;

    http://www.americanhvacparts.com/Mer...ct_Code=FUS286
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event